It has long been known that an increase in the speed and efficiency of many chemical reactions can be induced by subjecting the substances involved to greatly increased pressure and temperature conditions. At one time it was popular to develop the desired conditions by utilizing autoclaves to confine a batch of the material to be treated which, when heated, gave off vapors and pressurized the container. Alternatively, tanks were pressurized with pump while being heated.
Because of the lack of capacity due to the batch nature of the autoclave process, and because of the mechanical maintenance problems inherent in the use of specialized pumps and outlet throttling devices, the autoclave and pumped pressure tanks are being replaced by the art of using a hydraulic column to develop the desired pressure. The teachings in this art are typified by Bauer (U.S. Pat. No. 3,449,247), Lawless (U.S. Pat. No. 3,606,999), McGrew (U.S. Pat. No. 4,272,383), Burleson (U.S. Pat. No. 4,564,458) and Titmas (U.S. Pat. No. 4,594,164). All of these practice the use of a gaseous oxidant, such as air or oxygen, to heat the process by the destruction of the materials in a water based media.
Although the hydraulic column art eliminates the capacity problems of the autoclave and solves the additional autoclave problems of pressurizing and depressurizing, this art is plagued by the loss of desired materials inherent in the use of oxidation of the product stream to induce heat, and by the accumulation of partly decomposed debris on the annulus walls. Furthermore, only Burleson U.S. Pat. No. 4,564,458 and Titmas U.S. Pat. No. 4,594,164 teach the advantages of operation at supercritical water temperature and pressure conditions. But such conditions only magnify the aforementioned problems which are not addressed by these supercritical patents.
Other hydraulic column heat/pressure methods, such as Land et al. (U.S. Pat. No. 3,464,885) and Titmas (U.S. Pat. No. 3,853,759), do not utilize the oxidation of the product stream to induce heat. Both teach the use of steam to provide heat which is not practical in the supercritical range as the condensation of steam at the supercritical point or above transfers no heat to the process as there is no difference in heat content between steam and condensate under those conditions.
All of these one pass hydraulic column methods require that the downdraft stream be continually heated as it approaches the reaction chamber. But it is this preheating requirement which causes the problem of premature decomposition of the material and resultant accumulation of such material on the passage walls. Such problems are magnified when operating at the supercritical water temperature and pressure range because of the greater extent of the hydraulic column. No one has addressed the need to restrain the rate of heat rise in the downdraft column to avoid these problems, and then abruptly raise the temperature of the stream to the desired temperature.
The only art of which I am aware that has the capability to approach the required effect in the supercritical range is Modell (U.S. Pat. No. 4,338,199). The Modell patent does not teach the use of a hydraulic column to effect the necessary pressure but rather uses pumps to induce all the pressure in an above ground vessel and is thus plagued with the same problems as the autoclave. Furthermore, the excessive and inefficient energy demand required by the pumping process is not suitable for large volumes of fluid with particles of abrasive materials in suspension. In addition, Modell does not teach any suitable means to remove the various mixed material streams from the reaction chamber.